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  • By Pacific island Times News Staff

Palau's trochus growing in size and number

The population of trochus in Palau has been increasing in both size and number, according to a new study released by the Palau International Coral Reef Center (PICRC) and the Bureau of Marine Resources.

Trochus is a genus of top-shaped sea snails with an operculum and a pearly inside to their shells, marine gastropod molluscs in the family Trochidae, the top snails. Trochus niloticus, called "Semum" in Palauan, is a valuable reef gastropod because of its use for mother-of-pearl buttons, jewelry, handicrafts and polishing agents.

Results of the study show a significant increase in density, population abundance, and size in each of the habitats surveyed from 2016 to 2019.

The average size of all trochus counted was 9.34 cm, with 86 percent of the population greater than the legal harvest size of 3 inches (7.62 cm), and 48 percent of the population greater than 4 inches (10 cm).


During the last survey in 2016, trochus density at the reef crest was 146 individuals per hectare. This year’s survey, the number has increased by nearly 20 percent to 757 individuals per hectare.

Overall, trochus populations in Palau, both on the fore reef and reef crest habitats, is an estimated 3,385,995 individuals, where 2,909,980 individuals are of legal harvest size.

The study was conducted in 122 sites located in fore reef and reef crest habitats from Kayangel to Peleliu. This was the second follow up of the same study done by BMR in 2016.

"In 2016, the total reef area (both fore reef and reef crest) that was surveyed was 9,400 m2 (number of sites multiplied by the 100m2 ), where a total of 132.33 T. niloticus were counted. This total density was converted into number of individuals per hectares (ha), amounting to approximately 140.78 individual T. niloticus found in 1 ha or 10,000 m2," the PICRC report said.

"However, in 2019, the total reef area that was surveyed was 12,200 m2 , where a total T. niloticus individuals found were 628.33. Converting to hectares, a total of 515.03 T. niloticus individuals were recorded per 1 ha."

Based on the study, PICRC made the following recommendations:

* Allow harvest of T. niloticus for at least two weeks to enable residents to harvest, but also limit exploitation of the resource, allowing for a sustainable stock of trochus for further reproduction and future harvesting.

* Establish a monitoring protocol for T. niloticus to continually assess the stocks at least every two years. This will help keep the Congress and resource managers informed on the status and trends of trochus stocks through time, and to make informed decisions and find ways to sustainably manage the resources.

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